This invention relates to processes and apparatus used for cleaning heater tubes.
Heaters are used in petrochemical installations to heat fluids for a variety of purposes, typically to break apart larger hydrocarbon molecules into smaller molecules, The heaters contain tubes, up to and even more than a kilometer long in each of several passes, that pass first through a convection section of a heater and then through a radiant section. During use, the heater tubes gradually become contaminated on their insides. This contamination, often called coke, tends to degrade the efficiency of the heater over time and can eventually cause the heater to stop working.
Various methods are known for decoking heaters. In one method, the heater is shut down and steam cleaned with high pressure steam. In another method, described for example in U.S. Pat. No. 5,358,573 issued Oct. 25, 1994, by the same inventor, the heater is shut down and pigs with appendages run through the heater until it is clean. In another method, described in U.S. Pat. No. 5,186,815 issued Feb. 16, 1993, the heater tubes are treated while the heater is in operation by injecting solid particles of very small size into the heater tubes, recovering the solid particles at the outlet and recirculating the solid particles back to the inlet of the heater.
Use of pigs to clean heater tubes is very effective since the pigs have a robust scraping action. Heater operators in South America who have used the inventor""s method described in U.S. Pat No. 5,358,573 have asked the inventor to provide cleaning of the heater tubes by pigs while the heater is in operation. The inventor has thus come up with a novel solution to the problem of providing a heater cleaning operation by using pigs while a heater is in operation.
It is an object of this invention to provide a method and apparatus for pigging an operating heater. It is a further object of this invention to provide a pig launcher and receiver connected in parallel with tubing.
Therefore, there is provided in accordance with one aspect of the invention a method of cleaning tubing in an operating heater, in which the tubing has an inlet and an outlet, the method comprising repeating the steps of:
(A) while the heater is in operation, running a pig through the tubing from the inlet to the outlet; and
(B) returning the pig to the inlet along return tubing, in parallel connection to the heater tubing.
In accordance with a further aspect of the invention, a boost pump is connected to the return tubing via a boost pump connection pipe to provide pressure for returning the pig to the inlet.
In accordance with a further aspect of the invention, a pig is launched into one of the heater tubing and the return tubing by use of a pig launcher mounted parallel to the one of the heater tubing and the return tubing.
In accordance with a further aspect of the invention, the method further comprises removing the pig from one of the heater tubing and the return tubing with a pig receiver mounted parallel to the one of the heather tubing and the return tubing.
In accordance with a further aspect of the invention, a single combined pig launcher and receiver functions as the pig launcher and the pig receiver.
In accordance with a further aspect of the invention, the return tubing is closed by a return valve while the pig is running through the heater tubing, and the return valve is opened after the pig passes the boost pump connection pipe.
In accordance with a further aspect of the invention, the return tubing is connected to the outlet of the heater at a junction, and an outlet valve is provided on the outlet downstream of the junction, and the method further comprises the step of closing the outlet valve after the pig passes the boost pump connection pipe.
In accordance with a further aspect of the invention, when a pig enters the inlet to the heater tubing, after passing through the return tubing, the return valve is closed and the outlet valve is opened.
In accordance with a further aspect of the invention, there is provided apparatus for pigging heater tubing in an operating heater, the heater tubing having inlet tubing and outlet tubing. Return tubing is connected to the inlet tubing at a first junction and to the outlet tubing at a second junction. A boost pump is connected to the outlet tubing by a boost pump connection pipe. Pig launching and receiving equipment is connected for launching of pigs into and removal of pigs from the heater tubing and return tubing. An outlet valve is provide on the outlet tubing downstream of the second junction. A first pig tripper is provided on the outlet tubing downstream of the boost pump connection pipe. A return valve is provided on the return tubing. A second pig tripper is provided near the inlet tubing for detecting when the pig is close to the inlet tubing.
In accordance with a further aspect of the invention, the pig launching and receiving equipment comprises a pig launcher mounted parallel to one of the heater tubing and the return tubing; and a pig receiver mounted parallel to one of the heater tubing and the return tubing.
In accordance with a further aspect of the invention, there is provided a pig launcher and receiver comprising tubing in which fluids may flow; and a pig launcher and receiver body, the pig launcher and receiver body having an interior cavity for receiving pigs, and a motive fluid inlet and a motive fluid outlet, and a door for removal of pigs from and insertion of pigs into the pig launcher and receiver body. A basket is provided in the pig launcher and receiver body for holding pigs. An inlet pipe controlled by an inlet valve, preferably a three way full port valve, is connected to the tubing at a first Y junction and connected to the motive fluid inlet. An outlet pipe controlled by an outlet valve, preferably a three way full port valve, is connected to the tubing at a second Y junction and connected to the motive fluid outlet.
Preferably, the motive fluid outlet and the motive fluid inlet are located at opposite ends of the interior cavity.
In accordance with a further aspect of the invention, there is provided a method of cleaning a tube in an operating heater, wherein the tube has an inlet and an outlet and fluid being heated is flowing from the inlet to the outlet, the method comprising the steps of:
monitoring the temperature at the outlet of the tube; and
when the temperature at the outlet of the tube indicates a degradation of efficiency of the heater below a given set point, running a pig through the tube to clean the tube while the heater is operating.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.